The present invention relates to a control apparatus for a heat exchanger, which apparatus has a casing through which a first fluid flows and a tube disposed within the casing for a second fluid to flow therethough, allowing a heat exchange to occur between the first and second fluids; the control apparatus being so arranged as to alter the flow rate of the second fluid in accordance with a change in temperature of the first fluid, thereby maintaining the temperature of the first fluid at a constant level.
In a hydraulic apparatus having a circuit for supplying a working oil from a reservoir to a predetermined equipment, through a pump, and for returning the working oil from the predetermined equipment to the reservoir; the working oil is heated by compression in the pump and by the work performed in the equipment. If the temperature of the working oil greatly exceeds a given value, the performance of the working oil is degraded and, hence, the hydraulic apparatus will not attain a predetermined performance level. To avoid this outcome, the hydraulic apparatus has an oil cooler which serves to keep the working oil within a predetermined temperature range.
The oil cooler is a kind of heat exchanger and has a casing through which the working oil flows and a plurality of tubes disposed within the casing for a cooling medium, such as water, to flow therethrough. And, in this oil cooler, heat is conducted from the working oil serving as the first fluid to the cooling medium which serves as the second fluid, so that the temperature of the working oil falls.
In a hydraulic apparatus in which the work load of the working oil within a predetermined equipment frequently changes, increases in the temperature of the working oil are frequently subject to change. Therefore, such kind of hydraulic apparatus generally has a control apparatus for changing a flow rate of the cooling medium in the oil cooler in accordance with a change in temperature of the working oil, thereby keeping the working oil within the predetermined temperature range.
A conventional control apparatus consist of an electromagnetic valve which communicates with an inlet port of each of a plurality of tubes for channeling cooling water through the casing of the oil cooler and which serves to open/close the inlet port, and a temperature sensor for detecting the temperature of the working oil flowing into the casing of the oil cooler. And, when the temperature of the working oil falls below a predetermined value the electromagnetic valve closes the inlet port to stop the flow of the cooling medium in the oil cooler, and, when the temperature of the working oil has reached the predetermined value the temperature sensor supplies a signal to the electromagnetic valve to make the electromagnetic valve open the inlet port for allowing flow of the cooling medium.
In the conventional control apparatus having the construction described above, the electromagnetic valve and the temperature sensor must be separately disposed on the oil cooler. Furthermore, since an external power supply for driving the electromagnetic valve and a related electric circuit are required, the number of component parts is increased, resulting in a complex structure. Therefore, the manufacturing cost is increased, the assembly operation is time-consuming, and the control apparatus cannot be made compact.